Transmembrane proteins are key components of essential cellular functions. One particular class of transmembrane proteins, ion channels, are commonly characterized by the method utilized to open or close the channel protein, either permitting or preventing specific ions from permeating the channel protein and crossing the cellular membrane. For example, one type of channel protein is the voltage-gated channel protein, which is opened or closed in response to changes in electrical potential across the cell membrane. Another type of channel protein is mechanically gated, such that mechanical stress on the protein opens or closes the channel. Still another type is ligand-gated, such that it opens or closes depending on whether a particular ligand is bound the protein. The ligand can be either an extracellular moiety, such as a neurotransmitter, or an intracellular moiety, such as an ion or nucleotide.
Transmembrane proteins such as ion channels are involved in a wide variety of biological process, such as cardiac, skeletal, and smooth muscle contraction, nerve function, epithelial transport of nutrients and ions, T-cell activation and pancreatic beta-cell insulin release. For example, one common type of channel proteins, K+ ion channels, control heart rate, regulate the secretion of hormones such as insulin into the blood stream, generate electrical impulses central to information transfer in the nervous system, and control airway and vascular smooth muscle tone. Thus, K+ ion channels participate in cellular control processes that are abnormal, such as cardiac arrhythmia, diabetes mellitus, seizure disorder, asthma and hypertension.
In the search for new drugs, diagnostics, or research tools, transmembrane proteins are therefore a common target.